Corneal endothelial polymegathism (variation in cell size) appears to be associated with a loss of cell functional capacity (Rao et al., Ann. Ophthalmol., 1979; Shaw et al., Ophthalmol., 1978; Kaufman & Katz, Invest. Ophthalmol. Vis. Sci., 1977) resulting in edema and bullous keratopathy. It is disturbing therefore to find that polymegathous endothelial cells are induced by wearing contact lenses (Schoessler and Woloschak, Int. C.L. Clinic, 1981; Schoessler, Int. C.L. Clinic, 1983; Stocker and Schoessler, Invest. Ophthalmol. Vis. Sci., revised submission 1984). Since polymegathous endothelial cells increase the risk associated with corneal surgery (Rao et al., Ann. Ophthalmol., 1979), it is important that this phenomenon of contact lens induced endothelial pleomorphism be thoroughly investigated. The proposed plan calls for a four year monitoring of the corneal endothelium of a nonwearing control group and of other young phakic patients who will be fitted with contact lenses of varying oxygen transmissibilities for daily and extended wear. Wide field scanning microscopy will be used to document cell changes centrally and peripherally in the cornea. An objective individual cell area analysis will be accomplished by state-of-the-art computer techniques utilizing image analysis. Corneal thickness will be monitored throughout the study. Specific goals of the project are to discover the types of pleomorphic change (size & shape) induced by contact lenses, to plot the time course of development of endothelial change for the various lens types studied, to ascertain how the polymegathism develops, to test the hypothesis that the rate of development of polymegathism is related to lens transmissibility, to assess the reversibility of such contact lens induced endothelial pleomorphism, and to develop a model for predicting pleomorphic cell changes. Long term objectives are to identify contact lenses or contact lens characteristics which are not associated with the development of altered endothelial cells, and to relate endothelial appearance (pleomorphism) to endothelial functional status. Additional studies, such as this proposed investigation, have been recommended to investigate the biological effects of procedures and materials for lens correction of refractive error (National Plan, Vol. 2, Prt. 2, Pgs. 70-71, 1983-87). For rebuttal to previous SUMMARY STATEMENT, please see page 14.